1. Field of the Invention
This invention relates to a automatic guided vehicle traveling along a guide path and a method of controlling the automatic guided vehicle.
2. Description of Related Art
Typically, automatic guided vehicles are equipped with electric motors, such as, for example, a compound-wound motor comprising an armature, a series field system, a switch for the series field system, a shunt field system, a shunt field resistance and a switch for the shunt field system. This type of electric motor produces a regenerated current while the automatic guided vehicle runs on a downhill slope at a speed higher than a specified speed. The regenerated current is effectively used to turn on the shunt field switch with an amplified output from a voltage discriminator when it exceeds a specified level, short-circuiting the shunt field resistance to convert the shunt field system into an intensified field system, and hence to decrease the rotational speed of the armature so as to prevent the automatic guided vehicle from falling into reckless running. Such an automatic guided motor-driven vehicle is known from, for example, Japanese Patent Publication No. 61-48322.
According to the prior art automatic guided vehicle, while a regenerated current, or regenerated energy, is effectively used with an advantage of applying regenerative braking to the automatic guided vehicle, the regenerated current is hard to use for controlling a traveling direction of the automatic guided vehicle.
Japanese Patent Application No. 8-134485, filed by the same applicant of this application, describes a useful manner of regenerated current for controlling a automatic guided vehicle to travel along a prearranged path established by a guide means. The vehicle detects a lateral deviation from the path guide means by means of a magnetic sensor comprising a number of hole elements and controls regenerated current (regenerated braking force) of the right and left wheel drive motors by the pulse width modulation (PWM) method.
While controlling the regenerated current of the wheel drive motor is helpful in saving electric power of a battery and improves the performance of follow-up the path guide means during traveling flat path or a down slope, it is hard for regenerative braking to produce strong braking force when the automatic guided vehicle travels at lower speeds and to stop at an intended position.